As a semiconductor device used for power semiconductor devices, diodes and IGBTs (Insulated Gate Bipolar Transistor) having a withstand voltage of 400V, 600 V, 1200V, 1700V, 3300V or more are known. These diodes and IGBTs are used for power conversion devices, such as convertors and invertors, and are demanded to have low loss, low noise and high breakdown tolerance, as well as low cost. As an example of the semiconductor device used for power semiconductor devices, a pin (p-intrinsic-n) diode will be described.
FIG. 36 is a cross-sectional view depicting a key portion of a conventional diode. As illustrated in FIG. 36, in the conventional diode, a p-type layer (not illustrated) is selectively disposed on a front surface side of an n−-type semiconductor substrate to be an n−-type drift layer 101, and in the p-type layer, a p-type anode layer 102 is selectively disposed, and a termination withstand voltage structure is disposed on a periphery surrounding the p-type anode layer 102. On the rear surface side of the n−-type semiconductor substrate, an n+-type cathode layer 104 is disposed in a position on the opposite side of the p-type anode layer 102. The reference numeral 103 denotes an anode electrode, and 105 denotes a cathode electrode.
In the case of the conventional diode, a reverse recovery loss is reduced by introducing heavy metal or defects into the n-type drift layer 101, so that the carrier lifetime of the n−-type drift layer 101 is decreased, and annihilation of the carriers is quickened during reverse recovery. At this time, if a carrier lifetime distribution, in which the carrier lifetime on the cathode side of the n−-type drift layer 101 is longer than the carrier lifetime on the anode side, is created, reverse recovery current/voltage waveforms, where oscillation of current/voltage waveforms during reverse recovery or surge (current generated by a transition abnormal voltage) due to oscillation of voltage waveforms are hardly generated and recovery is soft, can be obtained.
According to a proposed semiconductor device, in which the carrier lifetime is controlled like this, (e.g. Patent Document 1 (paragraph 0037)), defects, which were formed in the drift region when hydrogen ions are irradiated from the rear surface of the silicon substrate, have a peak in a position deeper than the intermediate depth of the drift region from the substrate front surface, and recombination of the carriers in a position deeper than the intermediate depth of the drift region from the substrate front surface is accelerated, whereby the carrier lifetime control function is implemented.
According to another proposed device (e.g. Patent Document 2), lifetime of carriers near the pn junction between the p-type anode layer and the n−-type drift layer and the lifetime of carriers near the n−n+ junction between the n−-type drift layer and the n+-type cathode layer in the n−-drift layer are controlled by a double sided irradiation or protons, or by a double irradiation of protons and electron beams, so that the lifetime of carriers near the pn junction is controlled to be shorter than the lifetime of carriers near the n−n+ junction.
Patent Document 1: Japanese Patent Application Laid-open No. 2011-049300
Patent Document 2: Japanese Patent Application Laid-open No. H08-102545